Managing internet protocol unicast and multicast communications

ABSTRACT

A system for managing internet protocol of at least unicast and/or multicast communications over a network has a network interface  20  for interfacing between the network  10  and other parts of the system. An audio compression/decompression and packetising controller  30  is interposed between the interface  20  and an audio mixer  40  such that the network interface outputs audio signals to the audio mixer for mixing the audio signals at different respective audio levels. An audio channel manager is connected to the controller  30  and audio mixer  40  so as to dynamically allocate audio channels and for connecting the audio mixer to an allocated channel. A message manager  60  is connected to the network interface and to the audio channel manager for managing the unicast and/or multicast communication of the audio signals.

BACKGROUND OF THE INVENTION

1) Field of the Invention

This invention relates to a system and method for managing InternetProtocol unicast and multicast communications.

2) Description of the Related Art

Presently, systems exist to provide one-to-one, one-to-many andmany-to-one communications in a form often known as intercom, talkbackor conferencing. Such systems generally use vendor-specificinterconnections and dedicated hardware and/or software. These providetelephony-based multi-user “conferencing” and are available oncommercially available analogue or digital telephony systems as well asInternet Protocol (IP) based systems, commonly known as Voice-over-IP,or VoIP. All these known systems can provide communications betweensingle and multiple users.

IP-based systems presently rely on “call conferencing”. That is, to setup a conference, a conference initiator utilises functions of thetelephone or telephone application to call up the parties required. Eachparticipant, or conference member, connects to the conference using atelephone line or channel. At all times the members of the conferenceare determined and controlled by the conference initiator whoexclusively has the executive power to terminate the conference.Individual participants may leave at any time, but they cannot thenrejoin without intervention from the conference initiator.

In order that each conference member may hear other conference members,the audio received from all participants is mixed together at theinitiator's telephone/system and re-transmitted to the conferencemembers. This has the disadvantage that all members receive audio at afixed level controlled by the initiator's telephone/system. Additionallyeach member receives his own audio back again from the conferenceinitiator and then relies on the abilities of an echo canceller or other“ducking” and/or dimming techniques to reduce this to an acceptablelevel. Dimming is a technique whereby gain of an audio route istemporarily reduced to prevent howl-round.

Typical telephony and/or computer audio inputs also have poor controlover audio input levels allowing overload conditions to exist. In anattempt to prevent this, lower than ideal operating levels may be usedto leave high overload margins and therefore the system runs with anincreased noise floor.

In this way, the audio quality of the conference is compromised.

Moreover, the transmission of audio over an IP network using VoIPtechnology is generally undertaken using unicast, i.e. one-to-one,messaging. As the number of conference members increases, the networktraffic thereby necessarily increases.

SUMMARY OF THE INVENTION

There is, therefore, a requirement to provide communications for, butnot exclusively for, intercom and conferencing based on IP technologywhich provides the ability to mix a number of audio channels together toprovide a user with received audio from a number of different sources.

Such a system should desirably provide better control of the audiomixing and distribution functions in certain IP audio applications, withbetter overload control. Preferably each user should be provided withindependent control over received and transmitted audio channels, andtheir audio levels, so that mixing thereby becomes “distributed” betweenall participants. To reduce network loading, audio should be distributedbetween the participants using either unicast or multicast, i.e.one-to-many, addressing as appropriate to ensure minimal networktraffic.

This invention seeks to overcome the foregoing difficulties and achievethe above objects.

According to a first aspect of the invention there is provided a systemfor managing Internet Protocol of at least one of unicast and multicastcommunications over a network, the system comprising: network interfacemeans for interfacing between the network and other parts of the system;signal processing means connected to the network interface means havingat least one audio channel for decompressing and de-packetising audiosignals received from the network through the network interface meansand for outputting the audio signals to audio mixer means for mixing theaudio signals at different respective audio levels and having at leastone audio channel for compressing and packetising audio signals receivedfrom the audio mixer means mixed at different respective audio levelsfor transmission through the network interface means over the network;audio channel manager means connected to the signal processing means fordynamically allocating the audio channels in the signal processing meansand connected to the audio mixing means for signalling an allocatedchannel to the audio mixing means; and message manager means connectedto the network interface means and to the audio channel manager meansfor managing the at least one of unicast and multicast communication ofthe audio signals.

Conveniently, there is provided system controller means connected to themessage manager means and the audio channel manager means forconfiguring and controlling the message manager means and the audiochannel manager means.

Preferably, there is provided application program interface meansconnected to the system controller means for interfacing between thesystem controller means and an application program.

Conveniently, there is provided audio input and output interface meansfor interfacing between the audio mixer means and audio inputs andoutputs.

Advantageously, the audio input and output interface means comprise atleast one of audio limiting and compression means.

Advantageously, the message manager means includes means for determiningwhich remote systems may join and leave a communication session therebypreventing unauthorised monitoring of or contributions to thecommunication session.

According to a second aspect of the invention there is provided a methodfor managing Internet Protocol transmission of at least one of unicastand multicast communications over a network to a remote system,comprising the steps of: a) receiving an audio transmission request ataudio channel manager means to transmit an audio signal over the networkto a remote location; b) the audio channel manager means communicatingwith signal processing means to determine whether an appropriate audiocompression and packetisation channel is allocated within the signalprocessing means and if not establishing such a channel and instructingan audio mixer connected to the signal processing means thereof; c)message manager means connected to the audio channel manager meansdetermining whether a multicast session is established with the remotesystem and if it is established adding the address of the remote systemto an address list of the multicast session but if it is not establisheddetermining whether to establish a multicast session or a unicastsession as appropriate with the remote location and establishing a newmulticast session and adding the address of the remote location to anaddress list of the new multicast session or establishing a unicastsession as determined; d) using the signal processing means to compressand packetise the audio signal; and e) transmitting the compressed andpacketised audio signal over the network to the remote system.

Conveniently, step a) of receiving an audio request at audio managermeans includes the steps of providing system controller means connectedto the message manager means and to the audio channel manager means andproviding an application program interface between the system controllerand an application program, and receiving the audio transmission requestat the application program interface and passing the request through thesystem controller means to the audio channel manager means.

Advantageously, step d) of using the signal processing means to compressand packetise the audio signal further comprises the steps of providingaudio input and output means connected to the audio mixing means andreceiving an audio signal at the audio input and output means, limitingand/or compressing the audio signal and passing the signal to the audiomixing means for mixing the audio signal with other audio signals andpassing the mixed audio signals to the signal processing means.

Conveniently, step e) of transmitting the compressed and packetisedaudio signal, further comprises the steps of passing a compressed andpacketised audio signal from the signal processing means to an IPinterface means for transmission over the network.

Advantageously, the method includes the further step, after receipt ofthe audio transmission request, of determining whether communicationwith the remote system is permitted according to predetermined rules andeither allowing or aborting the audio transmission request accordingly.

According to a third aspect of the invention there is provided a methodfor managing the reception of at least one of unicast and multicastcommunications over a network, comprising the steps of: a) receiving anaudio reception request at audio channel manager means to receive anaudio signal over the network from a remote system; b) the audio channelmanager means communicating with signal processing means to determinewhether an appropriate audio de-compression and de-packetisation channelis allocated within the signal processing means and if not establishingsuch a channel; c) the audio channel manager means instructing an audiomixer of the allocated channel; d) receiving the audio signal at thesignal processing means; e) the signal processing means decompressingand depacketising the received audio signal in the allocated channel andoutputting the decompressed and de-packetised audio signal to the audiomixing means; and f) the audio mixing means mixing the received signalwith other received audio signals and outputting the mixed audio signalsto audio outputs connected to the audio mixing means.

Conveniently, the step of receiving an audio reception request at audiomanager means comprises the further steps of receiving an audioreception request over the network at IP interface means, passing therequest to the message manager means and the message manager meanspassing the request to the audio channel manager means.

Advantageously, step d) of receiving the audio signal comprisesreceiving the audio signal at the IP interface means and passing theaudio signal to the audio signal processing means.

Conveniently, there is provided a further step of providing systemcontroller means for controlling the message manager means and forcontrolling the audio channel manager means, the system controller meansinterfacing with an application program through application programinterface means connected to the system controller means.

Conveniently, there is provided a further step, after receipt of theaudio reception request, of determining whether communication with theremote system is permitted according to predetermined rules and eitherallowing or aborting the audio reception request accordingly.

BRIEF DESCRIPTION OF THE DRAWINGS

An embodiment of the invention will now be described by way of example,with reference to the accompanying drawings in which:

FIG. 1 is a block diagram of a system according to the presentinvention;

FIG. 2 is an exemplary interconnection diagram illustrating three of thesystems shown in FIG. 1 interconnected by an IP network;

FIG. 3 is a flowchart of the method of initiating audio communicationsaccording to an aspect of the invention;

FIGS. 4A & 4B are block diagrams illustrating audio paths establishedduring communications using the system and method of the invention; and

FIG. 5 is a flowchart according to another aspect of the inventionshowing the method of handling requests to receive audio communications.

In the figures like reference numerals denote like parts.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, a system 101 for managing Internet Protocol unicastand multicast communications includes an internet protocol (IP)interface 20 for connecting other parts of the management system 101 toan IP network 10 by means of a link 12. This interface may include, forexample, an ethernet, optical fibre or ATM physical interface and alsoIP stacks. The IP interface is connected by a link 21 to a signalprocessing module 30 for audio compression/decompression andpacketisation/de-packetisation. The signal processing module provides achoice of channels corresponding to different compression algorithms,e.g. ITU Recommendations G.711, G.722, G.728 and different audiopacketisation, for example, RTP: Real-time Transport Protocol, UDP: UserDatagram Protocol and AAL: Asynchronous Transfer Mode Adaption Layer.The signal processing module is connected by a link 31 to an audiomixing module 40 providing flexible audio mixing and routing functionswhereby 1 . . . n inputs can be mixed and routed to 1 . . . m outputswith fully variable individual gain values as set via the ApplicationProgram Interface (API). The audio mixing module 40 is further connectedby a link 41 to an audio input/output module 50 which typically providesanalogue to digital and digital to analogue conversion, audio filteringand input level limiting/compression. Input and output to the audioinput and output module is provided by a link 51 to a microphone andearphones 90 and by a link 52 to other audio input/outputs 91. The IPinterface 20 is further connected by a link 22 to a message managermodule. The signal processor module 30 and the audio mixer module 40 areconnected to an audio channel manager module 70 by links 32 and 42respectively. The audio channel manager module 70 is also linked to themessage manager module 60 by means of a link 61. A system control module80 is provided for controlling the message manager module and the audiochannel manager module by means of links 62 and 72 respectively. Thesystem control module is itself controlled by an application programinterface (API) linked to the system controller module by a link 82.

FIG. 2 shows a first, second and third systems 101, 102 and 103interconnected on the IP network 10. As shown in FIG. 2, the systems maybe connected via the Internet 11 if required. It is to be understoodthat the present invention can be utilised to establish communicationsbetween numerous further users, or systems, not shown in the Figure. Theinterconnection technology is not prescribed; the requirement on thenetwork is the ability to convey IP data packets for unicast and/ormulticast sessions. FIG. 2 illustrates an embodiment of the inventionusing three Personal Computers (PCs). It is to be understood that thepresent invention may have numerous other embodiments, not described indetail, such as:

-   non-PC hosted standalone embedded systems-   pure hardware (utilising electronic components)-   software-only systems running on a PC or dedicated computing    hardware.

The application program interface 85 is used to configure the system,providing information relating at least to an IP address of the systemand multicast address ranges. Additionally, security-related informationand the IP address of other users that each system may communicate with,and the manner in which they may communicate with each other (i.e.“rules”) are required. Such information is application-specific and notthe subject of this invention. It is assumed, for the purposes of thisdescription, that such configuration has been carried out and that allthree exemplary systems 101, 102, 103 shown in FIG. 2 may freelycommunicate, and have a method for establishing such communication.

The method of operation of the invention will now be described.

First System 101 Initiates Audio Transmission to Second System 102

Referring to FIG. 3, together with FIGS. 1 and 2, in order for the firstsystem 101 to initiate a request for audio communication with the secondsystem 102 through the API 85, a request for audio transmission is made,step 301. Security and authentication checks are carried out, step 302,by the message manager 60 exchanging unicast messages, using standardprotocols, such as TCP/IP between the first system 101 and the secondsystem 102 to verify that security rules imposed by the controllingapplication through the API, allow this communication to take place. Ifsuch checks fail, a message is sent, step 303, via the API to the user,or the user application program. Once verified that communication cantake place, the system controller 80 determines, step 304, through theaudio channel manager 70, whether a corresponding audio compression andpacketisation channel is allocated in the signal processing unit 30. Ifthe audio channel manager ascertains that no channel is allocated, theaudio channel manager will allocate, step 305, a compression andpacketisation channel in the signal processor module 30 and instruct,step 306, the audio mixer 40 appropriately. A number of differentcompression channels may be available in the signal processor module 30according to application requirements, each offering differentselectable compression algorithms and packetisation encapsulations. Theinitial negotiation with the remote second system 102 may determine therequired compression characteristics and packetisation requirements forthe communication. If an appropriate channel is not available, the errorcan be signaled via the API. The message manager 60 determines, step307, whether a multicast session is already established with the remotesecond system 102 and, if so, the destination address of the secondsystem 102 is added to a multicast list associated with the multicastsession. If no multicast session is already established, the messagemanager 60 determines, step 308, whether the audio communication shouldbe unicast or multicast, according, for example, to a history ofprevious audio communications from this source to other destinations, oraccording to other rules provided by the API. Normally a multicastsession is established, step 309, and an address list set up and amulticast address for second system 102 is added, step 310, to themulticast address list. The address of the multicast host is then sentto the second system 102 via the IP interface 20 and the second system102 is enabled to listen to the first system 101 on the host multicastaddress site and is thereby allowed to receive audio from the firstsystem 101. The first system 101 is thereby able to send, step 312, anaudio signal to the second system 102.

Audio signals may be input from a microphone 90 or from alternativeaudio inputs 91, through appropriate filtering and analogue to digitalconversion by the audio input and output module 50 and presented asinput to the digital audio mixing module 40. Input conditioning in theform of limiting or compressing is selectable to ensure that the maximumaudio level, once analogue to digital conversion has taken place, doesnot exceed a maximum coding range of the digital transmission system.

As shown in FIG. 5, the second system 102 will perform similar steps toreceive the audio signal. A request to accept audio communication isreceived, step 501, and security checks carried out, step 502, todetermine whether communication with the first system 101 is permitted.If not, a message is sent, step 503, to the API. Otherwise, thecorresponding audio channel manager module of the second system 102allocates, step 505, a decompression and de-packetisation channel in itssignal processing module and the audio channel manager takes the audiosignal from this channel and presents, step 506, the audio signal to theaudio mixer of the second system 102, which outputs signals to itsoutput audio devices. The API can be used to instruct the audio mixer toset the received level at a required value and to route the audio to anyavailable audio outputs. Thus, a unidirectional audio route may be setup from the first system 101 to the second system 102. The second system102 can chose to stop listening at any time to the first system 101without involving the first system 101. The second system 102 may stoplistening temporarily by instruction to the audio mixer or permanentlyby de-allocating the decompression and de-packetisation channel in itssignal processor module as instructed via the API. Unicast messagesbetween the two systems may be used to de-allocate channels as requiredand send status information via the APIs.

In order for the second system 102 to initiate audio transmission backto the first system 101, a duplicate, but independent, process occurs inreverse, and therefore, there is no inherent requirement in the presentinvention for audio to be transferred bi-directionally, in contrast tostandard telephony of the prior art, which utilises bidirectional(duplex) communications by default.

The First System 101 Initiates Audio Transmission to the Third System103

Referring to FIG. 4A, if the first system 101 wishes to communicate witha third system 103 at the same time as communicating with the secondsystem 102, an identical process to that used in establishingcommunications with the second system 102 takes place. However, in thiscase an audio communication session already exists from the first system101 to the second system 102.

Again, referring to FIG. 3, audio communications is requested, step 301.Security and authentication checks are made, step 302. If such checksfail, a message can be sent via the API, step 303, and the systemexited, step 313. Otherwise a check is made, step 304, to see whether anaudio compression and packetisation channel pre-exists. If not, such achannel is established, steps 305 and 306, including negotiation withthe remote third system 103; then, or if a channel does already exist, acheck on the pre-existence of a suitable multicast session is made, step307.

If a suitable multicast session exists, the required destination addressis added, step 310, to its multicast list; suitable unicast messagingtakes place to the destination to inform the third system 103 that audiowill be transmitted on the chosen multicast address and that the thirdsystem 103 should now listen to the multicast from this address.

If not, a decision on unicast or multicast audio transmission is made,step 308. If, as might occur in this example, a unicast transmission iscurrently established, the first system 101 is communicating with thesecond system 102, this transmission may be terminated and replaced by anew multicast session, or a second unicast session established. Themulticast or new unicast session are then established as appropriate,step 309 or 311, respectively. Finally audio transmission can takeplace, step 312.

The Third System 103 Initiates Audio Transmission to The Second System102

The third system 103 may for example also communicate with the secondsystem 102 using the same method.

Complete 3-Way Conference

If the steps above have been executed, all three parties are in audiocommunication as depicted in FIG. 4A and at this time there will bethree sessions in existence:

-   -   A first session 401 initiated by the first system 101 to send        audio to second and third systems 102 and 103,    -   A second session 402 initiated by the second system 102 to send        audio to the first system 101,    -   A third session 403 initiated by the third system 103 to send        audio to the second system 102.        The Third System 103 Initiates Audio Transmission to the First        System 101

It is possible to complete a full multi-party conference and allow allparties to communicate bi-directionally, as illustrated in FIG. 4B byadding a fourth session 404 from the second system 102 to the thirdsystem 103 and a fifth session 405 from the third system 103 to thefirst system 101. It is a function of the controlling application to dothis so it can be arranged for automatic reverse routes to be made, orfor manual reverse routes as required.

The method as described above and illustrated in the flowchart of FIG. 3is used by the third system 103 and the multicast audio transmissionsession managed by the third system 103 extended to include the firstsystem 101 as a destination. The negotiation with the first system 101results in the first system 101 allocating, step 305, anewde-packetisation and decompression channel.

The flowchart of FIG. 5 again illustrates the process in respect of thereception of audio signals by the first system 101, which is the same asthat described above for the receipt of audio signals by the secondsystem 102.

The third system 103 is in full control of received audio levels and mayjoin or leave the conference as required by the controlling application,not the initiating system.

The audio mix at the first system output has no component resulting fromlocal mixing of the first system's own audio input, nor any componentresulting from mixing at the remote second and/or third system(s). Audiothereby received is a clean “mix-minus”—a full mix of audiocontributors, minus the local source audio.

The audio communication paths resulting if all three exemplary systemsestablish bidirectional communications (i.e. a full duplex three-wayconference) is depicted in FIG. 4B.

Additional Flexibility and Functions

Flexibility exists in the system architecture to allow systems tocommunicate with others using different compression/decompression and/orpacketisation parameters. The signal processing module 30 can beinstructed, if required, to perform this function. In this mode, adifferent multicast list would be set up for each audio channelrequiring different parameters. Messages may be sent to listeningsystems to broadcast the availability of this audio using differentencoding parameters.

1. A system for managing Internet Protocol of at least one of unicastand multicast communications over a network, the system comprising:network interface means for interfacing between the network and otherparts of the system; signal processing means connected to the networkinterface means having at least one audio channel for decompressing andde-packetising audio signals received from a plurality of remote systemsthrough the network interface means and for outputting the audio signalsto audio mixer means for mixing the received audio signals at differentrespective audio levels relative to the respective remote systems suchthat a resultant audio mix has no component resulting from local mixingof the system's own audio input, nor any component resulting from mixingat the respective remote systems so that the audio mix is a full mix ofaudio signals from the remote systems mixed by the system with no localsource audio and having at least one audio channel for compressing andpacketising audio signals received from the audio mixer means mixed atdifferent respective audio levels for transmission through the networkinterface means over the network; audio channel manager means connectedto the signal processing means for dynamically allocating the audiochannels in the signal processing means and connected to the audiomixing means for signalling an allocated channel to the audio mixingmeans; and message manager means connected to the network interfacemeans and to the audio channel manager means for managing the at leastone of unicast and multicast communication of the audio signals.
 2. Asystem as claimed in claim 1 wherein there is provided system controllermeans connected to the message manager means and the audio channelmanager means for configuring and controlling the message manager meansand the audio channel manager means, autonomously and independently ofthe remote systems.
 3. A system as claimed in claims 1 wherein there isprovided application program interface means connected to the systemcontroller means for interfacing between the system controller means andan application program.
 4. A system as claimed in claim 1 wherein thereis provided audio input and output interface means for interfacingbetween the audio mixer means and audio inputs and outputs.
 5. A systemas claimed in claim 4 wherein the audio input and output interface meanscomprise at least one of audio limiting and compression means.
 6. Asystem as claimed in claim 1 wherein the message manager means includesmeans for determining which remote systems may join and leave acommunication session thereby preventing one of unauthorised monitoringof, and unauthorised contributions to, the communication session.
 7. Amethod for managing Internet Protocol transmission of at least one ofunicast and multicast communications over a network to a remote system,comprising the steps of: a) receiving an audio transmission request ataudio channel manager means to transmit an audio signal over the networkto a remote location; b) the audio channel manager means communicatingwith signal processing means to determine whether an appropriate audiocompression and packetisation channel is allocated within the signalprocessing means and if not establishing such a channel and instructingan audio mixer connected to the signal processing means thereof; c)message manager means connected to the audio channel manager meansdetermining whether an existing multicast session is established withthe remote system and if it is established adding the address of theremote system to an address list of the existing multicast session butif it is not established determining whether to establish a newmulticast session or a unicast session as appropriate with the remotelocation and if so establishing the new multicast session and adding theaddress of the remote location to an address list of the new multicastsession or establishing the unicast session; d) using the signalprocessing means to compress and packetise the audio signal; and e)transmitting the compressed and packetised audio signal over the networkto the remote system; such that an audio mix at the remote system has nocomponent resulting from local mixing of the remote system's own audioinput, nor any component resulting from mixing at other systems so thatthe audio mix is a full mix of audio signals from systems mixed by theremote system with no local source audio.
 8. A method as claimed inclaim 7 wherein step a) of receiving an audio request at audio managermeans includes the steps of providing system controller means connectedto the message manager means and to the audio channel manager means andproviding an application program interface between the system controllerand an application program, and receiving the audio transmission requestat the application program interface and passing the request through thesystem controller means to the audio channel manager means.
 9. A methodas claimed in claim 7 wherein step d) of using the signal processingmeans to compress and packetise the audio signal further comprises thesteps of providing audio input and output means connected to the audiomixing means and receiving an audio signal at the audio input and outputmeans, limiting the audio signal and passing the signal to the audiomixing means for mixing the audio signal with other audio signals andpassing the mixed audio signals to the signal processing means.
 10. Amethod as claimed in claim 7 wherein step e) of transmitting thecompressed and packetised audio signal, further comprises the steps ofpassing a compressed and packetised audio signal from the signalprocessing means to an IP interface means for transmission over thenetwork.
 11. A method as claimed in claim 7 including a further step,after receipt of the audio transmission request, of autonomouslydetermining whether communication with the remote system is permittedaccording to predetermined rules and either allowing or aborting theaudio transmission request accordingly.
 12. A method as claimed in claim7 wherein step d) of using the signal processing means to compress andpacketise the audio signal further comprises the steps of providingaudio input and output means connected to the audio mixing means andreceiving an audio signal at the audio input and output means,compressing the audio signal, and passing the signal to the audio mixingmeans for mixing the audio signal with other audio signals and passingthe mixed audio signals to the signal processing means.
 13. A method formanaging reception of at least one of unicast and multicastcommunications over a network from a plurality of remote systems,comprising the steps of: a) receiving an audio reception request ataudio channel manager means to receive one or more audio signals overthe network from a remote system; b) the audio channel manager meanscommunicating with signal processing means to determine whether anappropriate audio de-compression and de-packetisation channel isallocated within the signal processing means and if such a channel isnot established, establishing the channel; c) the audio channel managermeans notifying an audio mixer of the allocated channel; d) receivingthe audio signal at the signal processing means; e) the signalprocessing means decompressing and de-packetising the received audiosignal in the allocated channel and outputting the decompressed andde-packetised audio signal to the audio mixing means; and f) the audiomixing means mixing the received signal with other received audiosignals from the plurality of remote systems and outputting the mixedaudio signals to audio outputs connected to the audio mixing means; suchthat a resultant audio mix has no component resulting from local mixingof the system's own audio input, nor any component resulting from mixingat the respective remote systems so that the audio mix is a full mix ofaudio signals from the remote systems mixed by the system with no localsource audio.
 14. A method as claimed in claim 13 wherein the step ofreceiving an audio reception request at audio manager means comprisesthe further steps of receiving an audio reception request over thenetwork at IP interface means, passing the request to the messagemanager means and the message manager means passing the request to theaudio channel manager means.
 15. A method as claimed in claim 13 whereinstep d) of receiving the audio signal comprises receiving the audiosignal at the IP interface means and passing the audio signal to theaudio signal processing means.
 16. A method as claimed in any of claim12 wherein there is provided a further step of providing systemcontroller means for controlling the message manager means and forcontrolling the audio channel manager means, the system controller meansinterfacing with an application program through application programinterface means connected to the system controller means, operatingindependently of remote systems.
 17. A method as claimed in any of claim12 wherein there is provided a further step, after receipt of the audioreception request, of determining whether communication with the remotesystem is permitted according to predetermined rules and either allowingor aborting the audio reception request accordingly.